IXOIXO and strong gravityand strong gravity Measuring the black hole Measuring the black hole spinspin
GiorgioGiorgio MattMatt (Dipartimento di Fisica ‘Edoardo Amaldi’, (Dipartimento di Fisica ‘Edoardo Amaldi’, Università degli Studi Roma Tre) Università degli Studi Roma Tre)
The importance of spin The importance of spin measurements measurements
Why is important to know the BH spin distributions?
In AGN, it can discriminate between
different growth histories (spin is mainly acquired during the SMBH
evolution)
In GBHS, it tells us about the origin of
the BH (spin is mainly pristine)
Berti & Volonteri 2008
Accretion discsAccretion discs
We can assume that the inner disc radius
corresponds to the innermost stable circular
orbit (ISCO)
The ISCO depends on the BH spin and on whether the
disc is co- or counter-rotating with the BH
NB: a≤0.998, RISCO=1.237 (Thorne 1973)
Let us assume a geometrically thin, optically thick accretion disc. Matter rotates in (quasi) circular orbits (i.e. Vφ >> Vr ) with
Keplerian velocities.
Techniques Techniques
(Iron) line spectroscopy (GBH, AGN)
Continuum spectroscopy (GBH)
Timing (GBH, AGN)
Polarimetry (GBH, AGN)
NB: All these techniques are (mainly) based on the dependence of ISCO (in units of the
gravitational radius) on spin
Why IXO Why IXO
Large collecting area !!!!!!
All different techniques can be applied thanks to:
Broad band (0.3-40 keV)
Moderate to high spectral resolution
High count rates detector
Polarimetry
X-ray emissionX-ray emissionThe standard explanation for the hard X-ray emission in AGN and GBHS is Comptonization of disc photons by hot
(T=100-200 keV) electrons in a corona (e.g. Haardt & Maraschi 1991). The resulting spectrum is, in the first approximation, a power low with a high energy cutoff.
In GBHS, the thermal component is also in the X-ray band, extending up to several keV when in soft state.
UV/soft X
X-ray emissionX-ray emissionThe standard explanation for the hard X-ray emission in AGN and GBHS is Comptonization of disc photons by hot
(T=100-200 keV) electrons in a corona (e.g. Haardt & Maraschi 1991). The resulting spectrum is, in the first approximation, a power low with a high energy cutoff.
In GBHS, the thermal component is also in the X-ray band, extending up to several keV when in soft state.
Line Line profilesprofiles
(Fabian et al. 2000)
SR and GR effectsmodify the line profilein a characteristic and well-recognizable way
Advantages of the method are:
Intrinsic emission is known
Independent of the black hole
mass (radius is measured in
units of the gravitational radius)
a=1
a=0
ObservationObservationss
MCG-6-30-15
ASCA (Tanaka et al. 1995)
BeppoSAX (Guainazzi et al. 1999)
XMM-Newton (Wilms et al. 2001)
Rin <6, a>0 !!!
Rin > 6
Is MCG-6-30-15 unique ?Is MCG-6-30-15 unique ?
(Fabian et al. 2009)
1H 0707-495
Iron L line
SWIFT J1247 (Miniutti et al. 2010)
Fairall 9 (Schmoll et al. 2010)
NB: results obtained by fitting simulateneously
the line and the reflection continuum
ObservationObservations:s:
GBHCGBHC
XTE 1650-500(Miniutti et al. 2003)
GRS 1915-105(Martocchia et al.
2002)
GX 339-4(Miller et al. 2004)
ObservationObservations:s:
GBHCGBHC
Miller et al. 2009
(see also Ng et al. 2010 andMiller et al. 2010)
Continuum spectroscopyContinuum spectroscopy
R
RISCO
Much work by McClintock, Narayan et al.
Fitting the disc thermal emission provides a measurement of ISCO.
Requires:a) Spectrum dominated by thermal emission (soft state)
b) A very good modelling of the emissionc) Accurate values of M, i, D
R/M(G/c2)
0.10
0
0.05
a* = 0.98
a* = 0.9
a* = 0.7
a* = 0
dF/d
(lnR
)
Strong dependence on RISCO and
thence on the spin
Spin Results to DateSpin Results to Date
McClintock et al. (2011)
Different methods give different results…Different methods give different results…
Thermal continuum method
Disk reflection method
Miller et al. (2009)
(but recently the results of the two methods on J1550 have been
reconciled by Steiner et al. 2010)
QPOsQPOs
Stella & Vietri 1998+
Zhang et al. 1998
The mass of the black holeis needed to derive the spin
Orbiting spotsOrbiting spots
Courtesy of M. Dovciak
From time resolved spectroscopy it is possible to derive the radius both in units of the BH mass and
in standard units BH mass (and l.l. to the spin)
Orbiting spotsOrbiting spots
Dovciak et al. 2008
Iwasawa et al. (2004) find in the XMM-Newton data of NGC 3516 evidence for a possible 25 ks periodicity of
one of these features.
Observations: NGC 3516Observations: NGC 3516
The derived BH mass is
1-5 x 107
solar masses
consistent with other estimates
Strong gravity effects on Strong gravity effects on polarizationpolarization
General and Special Relativity significantly modifies the polarization properties of the radiation.
In particular, the Polarization Angle (PA) as seen at infinity is rotated due to aberration (SR) and light bending (GR) effects (e.g.
Connors & Stark 1977; Pineault 1977). The rotation is larger for smaller radii and higher inclination angles
(Connors, Stark & Piran 1980)
Newtonian- - - - - - - - - - - - - - - - - - - - - - -
Orbiting spot with:a=0.998; R=11.1 Rg
i=75.5 deg
(Phase=0 when the spot is behind the BH).
The PA of the net (i.e. phase-averaged)
radiation is also rotated!
Galactic BH binaries in high Galactic BH binaries in high statestate
GRS 1915+105(Done & Gierlinski 2004)
Connors & Stark (1977)
X-ray emission in Galactic BH binaries in soft states is dominated
by disc thermal emission, with T decreasing with radius.
A rotation of the polarization angle A rotation of the polarization angle with energy is therefore expected.with energy is therefore expected.
We (Dovciak et al. 2008) revisited and refined these calculations (see
also Li et al. 2008, Schnittman & Krolik 2009).
Detectability of the effect with IXO
Strongly dependent on
the spin of the BH !!
(Independent of the black hole
mass
GR effects: light bending GR effects: light bending model model
Variations of h have been suggested to be the cause of the puzzling temporal behaviour of the iron line in MCG-6-30-15 (Miniutti et al. 2003), where the line flux varies much less than the primary power law flux. This situation is expected in the aborted jet models for the corona (e.g. Ghisellini et al. 2004).
PLC
Fe line
Polarization of reflected Polarization of reflected radiation radiation
The polarization degree and angle depend on both h and the incl. angle (the latter may be
estimated from the line profile; for
MCG-6-30-15 is about 30 degrees,
Tanaka et al. 1995)
Variation of h with Variation of h with time/flux implies a time/flux implies a time/flux variation time/flux variation of the degree and of the degree and
angle of angle of polarizationpolarization
Dovciak et al. 2004, 2011
Polarization of reflected Polarization of reflected radiation radiation
The polarization degree and angle depend on both h and the incl. angle (the latter may be
estimated from the line profile; for
MCG-6-30-15 is about 30 degrees,
Tanaka et al. 1995)
Variation of h with Variation of h with time/flux implies a time/flux implies a time/flux variation time/flux variation of the degree and of the degree and
angle of angle of polarizationpolarization
Dovciak et al. 2004, 2011
SummarySummary
Thanks to the combination of large collecting area and of spectroscopic, timing and polarimetric capabilities,
IXOIXO will be able to measure the spin of the black hole in both GBHS and AGN in several different,
independent ways.
